Method for controlling a crane actuator

ABSTRACT

The invention relates to a method and an apparatus for controlling an actuator ( 7, 8 ) of a crane by control means ( 10 ) in a situation where the lifting power of the actuator ( 7, 8 ) of the crane is increased temporarily by an auxiliary valve arrangement ( 11 ). In the invention, control properties of the actuator ( 7, 8 ) are changed when the temporarily increased lifting power is applied to limit the speed of the actuator ( 7, 8 ).

BACKGROUND OF THE INVENTION

The invention relates to a method according to the preamble of claim 1and an apparatus according to the preamble of claim 7 for controlling aboom arrangement of a crane. The invention particularly relates to amethod and apparatus for controlling an actuator of a crane by controlmeans in a situation where the lifting power of the actuator of thecrane is temporarily increased by means of an auxiliary valvearrangement.

Transport vehicles, for example log trucks and various lumberingmachines, are equipped with loading cranes, the main purpose of which isto move, load or unload a load or perform other similar measures. Aloading crane may also be utilized in other tasks essentially related tothe work, where a heavy load is moved to improve working conditions orto reduce work-related expenses, an example of which is the avoidance ofdifferent road taxes dependent on the length of an articulated vehicleby lifting, for instance, a semi-trailer onto the cargo space of thevehicle body when there is no actual transportable load in the cargospaces of the vehicle or its trailer. By lifting the semi-trailer ontothe cargo space on top of the vehicle body, the length of the vehiclebecomes essentially shorter and the road tax is lower when the vehicleis transported on a road. Depending on the weight of the semi-trailer,it is often necessary to temporarily increase the lifting power of thecrane when the semi-trailer is lifted onto the vehicle body. Since thelifting power can be increased temporarily, it is thus possible to avoidthe purchase of a crane having a higher lifting power and being thusheavier and more expensive in terms of both the purchase price and theoperating costs only because the increased lifting power is requiredtemporarily.

The design of loading crane constructions is based on standards, whichdefine the calculation basis for the structures of mechanical partsaccording to the desired lifting power, load and work rotations, liftingclass, load group and method of application, for instance. Thecalculation basis also includes dynamic coefficients. Dynamiccoefficients define, for instance, lifting power and gravitational forceeffects of the crane parts and the load, i.e. the total load, andeffects of total load acceleration or deceleration. The dynamiccoefficient thus affects the lifting class of the crane, which, in turn,affects material selections and other cost factors associated with cranemanufacture. The manufacture. The service life of the crane is affectedby stress accumulations directed at the crane structures and formedduring loading. The stress accumulation is in practice influenced by thestatic maximum stress level during the crane operation, which, in thiscase, is defined on the basis of the hydraulic operating pressure usedin the crane, and by dynamic stress peaks occurring during theoperation, which are due to accelerations or decelerations of the totalload. The method and apparatus of the invention may affect the stressaccumulation during load and work rotations in such a manner that theservice life does not become essentially shorter, although the liftingpower is temporarily increased. This property may be utilized duringloading in situations where the normal lifting power of the crane is notsufficient for lifting a big load but there is a need for temporarilyincreasing the lifting power, whereupon the possibility to temporarilyincrease the lifting power of the crane without essentially shorteningthe service life of the crane allows to avoid the purchase of a biggerand thus more expensive and heavier crane.

In known solutions, to solve the above problem there is provided amethod and a control apparatus, in which there is a separateactuator-specific pressure relief valve for increasing the lifting powerin a pressure medium space on the operation side, i.e. on the pistonside, of the lifting cylinder. A separate pressure relief valve isadjusted to an actuator-specific pressure level determined by normalpressures, i.e. normal lifting power. Likewise, said separate pressurerelief valve is provided with a directional control valve, which may becontrolled electrically to provide the actuator with a higher pressurelevel, if desired. The control apparatus of the crane also comprises thecrane's actual control valve, the piston side of the lifting cylinder ofwhich comprises an actuator-specific pressure relief valve, which isadjusted to the pressure level determined by the increased liftingpower. By setting the separate directional control valve to an openposition, the pressure level of the actuator-specific, separate pressurerelief valve is determined as decisive, in this case as equivalent tothe normal pressure level. By setting the separate directional controlvalve to a closed position, the actuator-specific pressure level isdetermined to have the pressure level determined by theactuator-specific pressure relief valve of the actual control valve,which in this case corresponds to the increased lifting power. Inaddition to the above arrangement, the hydraulic circuit of the crane isprovided with a bypass flow control valve in a pressure line between apump and the actual control valve in such a manner that an control valvein such a manner that an amount of the pump output preset in the bypassflow control valve may be guided electrically directly to a return lineof the pressure medium. This arrangement aims at lowering the crane'sspeed of motion in cases where the crane is driven with the increasedlifting power. The objective has been to reduce stress peaks caused byaccelerations and decelerations of steering movements by lowering thecrane's speed of motion. In addition to the above, the hydraulic circuitof the crane is provided, in the pressure line between the pump and theactual control valve, with a separate main-pressure relief valve, whichhelps to determine the maximum pressure level for the entire hydrauliccircuit of the crane. The separate main-pressure relief valve isadjusted to a pressure level determined by normal pressures, i.e. thenormal lifting power. In connection with the separate main-pressurerelief valve there is also provided a directional control valve, whichmay be electrically controlled when the crane should be provided with ahigher pressure level. In connection with the actual control valve ofthe control apparatus of the crane there is a main-pressure reliefvalve, which is adjusted to a pressure level determined by the increasedlifting power. By setting the directional control valve in connectionwith the separate main-pressure relief valve to an open position, thepressure level of the separate main-pressure relief valve is determinedas decisive, in this case as equivalent to the normal pressure level. Bysetting the directional control valve to a closed position, the pressurelevel of the crane is determined to have the pressure level determinedby the main-pressure relief valve of the actual control valve, which inthis case corresponds to the increased lifting power. Bothabove-mentioned directional control valves are controlled synchronously,whereby the pressure level determined by the separate, actuator-specificmain-pressure relief valve and that determined by the separatemain-pressure relief valve correspond to one another.

A problem with the above-mentioned implementation is that stress peaksof the structures due to accelerations or decelerations of the totalload during the crane operation are particularly caused by pressurepeaks occurring on the piston side of the lifting cylinder. The mostsignificant factor in causing pressure peaks particularly during thelowering of the load is the design of the guide edges of the spindle ofthe actual control valve, particularly when it comes to the spindle partdetermining the control properties when the pressure medium is guidedfrom the piston side of the lifting cylinder along the return line tothe tank. In the above-mentioned implementation, the bypass flow controlvalve does not affect the pressure medium flowing from the piston sideof the lifting cylinder to the return line, which means that it does noteither affect the speed at which the load is lowered downwards or itsdeceleration or the stress peaks higher than normal pressure, which aredue to the acceleration or deceleration caused by the increased pressurelevel and the corresponding load, whereby the service time of the cranealso becomes shorter.

There are also systems, in which the increased lifting power isimplemented by means of control electronics and sensors of the crane.Patent WO9319000 discloses an implementation, in which the pressure ofthe operation side of a lifting cylinder is monitored by a pressuresensor. On the basis of signals of the pressure sensor and an anglesensor mounted in a boom arrangement, software controls the componentsof the crane hydraulic system according to a certain logic and providesan increased pressure level and reduced speeds of motion for theactuators of the crane, when the conditions defined in the software arefulfilled.

A problem with the above implementation is that the apparatus requires alot of electronics, sensors and other equipment necessary for buildingan electronic apparatus. Consequently, the system is expensive in termsof both a purchase price and maintenance costs. An electronicimplementation is also susceptible to faults when compared with amechanical system, in which hydraulic components are controlled bysimple electrotechnics.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object of the invention to provide a method and anapparatus implementing the method so that the above problems can besolved. The object of the invention is achieved by a method according tothe characterizing part of claim 1, which is characterized by changingcontrol properties of the actuator when the temporarily increasedlifting power is applied to limit the speed of the actuator. The objectof the invention is achieved by an apparatus according to thecharacterizing part of claim 7, which is characterized in that theactuator-specific auxiliary valve arrangement also comprises means forchanging control properties of the actuator in such a manner that thespeed of the actuator may be limited.

The preferred embodiments of the invention are disclosed in thedependent claims.

The invention is based on the idea that during loading or an auxiliaryfunction which is otherwise essentially associated with the operationand where a load exceeding the normal lifting power of the crane islifted or moved, a temporarily higher lifting power may be arrangedwithout shortening the service life of the crane. The highest stresspeaks occur at that point of work rotation when the load is guided withthe lifting cylinder of the crane downwards and the load is deceleratedquickly. Because the operation of the hydraulic pressure relief valvesis slow, the pressure in the actuator, in this case on the piston sideof the lifting cylinder, rises temporarily high during the decelerationand thus causes a momentary stress peak in the structures of the crane.

The method and apparatus of the invention affect the stress accumulationin such a manner that the crane is provided with an auxiliary valvearrangement, by which the crane may be provided with a temporarilyhigher lifting power and the control properties of the crane may bechanged when the higher lifting power is applied such that the excessivepressure rise in connection with changes in the speed of motion of theactuator and thus the occurrence of corresponding stress peaks may beprevented. Stress peaks are prevented when the crane is driven at theincreased pressure level so that return oil from the operation space ofthe actuator or flowing from the actual control valve of the crane tothe operation space of the actuator or other similar hydraulic fluid ischoked by a choke or other similar series flow control valve or meansand a directional control valve in parallel with the choke in such amanner that the actuator-specific speed of the lifting cylinder islimited to a value which does not cause an excessive increase in thestress peaks caused by the acceleration or deceleration of the totalload. In addition, the auxiliary valve arrangement is provided withpressure relief valves required for temporarily changing the mainpressure level of the crane and the actuator-specific pressure level anddirectional control valves controlling the use of the pressure reliefvalves. In this context, a limited speed refers to a speed which islower than the normal speed of the actuator when the normal liftingpower of the crane is applied. An operation space of the actuator refersto the side carrying the load of the actuator, which may be, in thecylinder, either the piston side of the cylinder, the piston rod side ofthe cylinder or the load may even be reversible, even be reversible,which means that the operation space of the cylinder may change atdifferent points of the actuator movement from one piston side to theother. Thus, the apparatus and method of the invention may be appliedeither on the piston side or on the piston rod side.

BRIEF DESCRIPTION OF THE INVENTION

The invention will now be described in greater detail in associationwith the preferred embodiments and with reference to the attacheddrawings, in which

FIG. 1 shows a prior art loading crane;

FIG. 2 shows a hydraulic chart of an apparatus of the invention. In thefigure, directional control valves of an auxiliary valve arrangement ofa hydraulic circuit are in the positions they have when the crane isdriven at the normal pressure level; and

FIG. 3 shows a hydraulic chart of an apparatus of the invention. In thefigure, directional control valves of an auxiliary valve arrangement ofa hydraulic circuit are in the positions they have when the crane isdriven at an increased pressure level.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a prior art loading crane, the base of which is fixed to avehicle or the like. A boom arrangement of the crane is mounted on thebase 1 in such a manner that the boom arrangement of the crane helps tomove, load or unload a load or to perform other similar measures. Inthis solution shown by way of example, the boom arrangement of the cranecomprises a post 2 provided on the base 1 and mounted to be turnedessentially around the vertical axis with respect to the base 1. Alifting boom 3, the movement of which with respect to the post 2 iscontrolled by a lifting cylinder 7, is in functional connection with thepost 2. The lifting boom 3 is functionally connected to the post 2 by ajoint 12 in such a manner that it can turn with respect to the post 2.The lower end of the lifting cylinder 7, by which the lifting boom 3 ismoved with respect to the post 2, is articulated with the lower end ofthe post 2 by a joint 28, and the upper end of the lifting cylinder isarticulated with the lifting boom 3, respectively, by a second joint 9.In turn, a transfer boom 4, whose movement with respect to the liftingboom 3 is controlled by a transfer cylinder 8, is functionally connectedto the lifting boom 3. According to FIG. 1, the free end of the transferboom 4 is equipped with an extension 5, to which a an extension 5, towhich a clamshell bucket 6 is connected for grabbing the load. The craneboom arrangement 2, 3, 4, 5 and 6 is controlled by the cylinders 7 and 8connected to control means 10 and by cylinders of the extension 5 andthe clamshell bucket 6.

FIG. 2 schematically illustrates a hydraulic chart for the control ofthe crane boom arrangement, where control means 10 are provided forcontrolling the lifting cylinder 7 and other actuators of the crane. Asto the control of actuators other than the lifting cylinder, thehydraulic chart is simplified. In this embodiment, the control meanscomprise the actual control valve 10, a main-pressure relief valve 17,an actuator-specific spindle 27, which in this case controls the liftingcylinder 7, and actuator-specific pressure relief valves 19, 22, whichtogether form the actual control valve of the crane. In addition, thecontrol means comprise actuators, i.e. cylinders. In addition to theseprior art control means, the apparatus according to the presentinvention comprises an auxiliary valve arrangement 11 arranged in thehydraulic circuit of the crane. The auxiliary valve arrangement 11comprises a directional control valve 24 connected in parallel with apressure medium space 15 between a pump 13 and the actual control valve10 of the crane and used for determining whether a pressure relief valve18 between this directional control valve 24 and a return line 16 is inor out of use. Furthermore, a directional control valve 23 and a choke26 in parallel with the directional control valve 23 are arrangedbetween the actuator connection of the crane's actual control valve 10,guiding the pressure medium to the piston side of the lifting cylinder7, and the connection on the piston side of the lifting cylinder 7.Furthermore, in parallel with the pressure medium space between thelifting cylinder 7 and the directional control valve 23 and the choke 26there is a directional control valve 25, by which it is determinedwhether a pressure relief valve 21 between the directional control valve25 and the return line 16 is in or out of use. Furthermore, a pressurerelief valve 20 is arranged in the pressure medium space between theconnection on the piston side of the lifting cylinder 7 and theabove-mentioned directional control valve 25. In this example, alldirectional control valves 23, 24, 25 are controlled electrically. Thepressure relief valves 17 and 18 of the above arrangement determine themain pressure level of the crane during loading. The pressure reliefvalves 19, 20, 21 determine the actuator-specific maximum pressurelevel, in this case that of the space on the piston side of the liftingthe space on the piston side of the lifting cylinder 7, by protectingthe actuator against external overload, for example.

The pressure levels of the pressure relief valves 17, 18, 19, 20, 21 areset in such a manner that the main-pressure relief valve 18 is set tocorrespond to the main pressure level according to the normal liftingpower, whereas the main pressure level corresponding to the increasedlifting power is set in the main-pressure relief valve 17. Likewise, theactuator-specific pressure relief valve 21 is set to correspond to thepressure level according to the normal lifting power, whereas thepressure relief valves 19 and 20 are set to the pressure levelcorresponding to the increased lifting power.

FIG. 2 shows a hydraulic chart in a form in which the crane is drivenwith the normal lifting power. When the crane is controlled with thenormal lifting power, in this case at the normal pressure level, thecontrol chart a of the directional control valve 24 is applied and themaximum pressure level of the pump pressure line 15 is defined accordingto the pressure level set in the pressure relief valve 18. When thelifting cylinder 7 is driven in the direction in which the total load islifted, the pressure medium produced by the pump is guided via anactuator-specific spindle 27 of the actual control valve 10, where theposition a is applied, to the piston side of the lifting cylinder 7 insuch a manner that the pressure medium passes via both the directionalcontrol valve 23, where the control chart a is applied, and the choke 26in parallel with it to the operational connection of the cylinder. Theoperational connection of the cylinder is protected by means of theactuator-specific pressure relief valve 21 in such a manner that thecontrol chart a of the directional control valve 25 is applied. Theactuator-specific maximum pressure level is thus defined according tothe pressure level set in the actuator-specific pressure relief valve21. When the lifting cylinder 7 is driven in the direction in which thetotal load is lowered, the pressure medium produced by the pump isguided via the actuator-specific spindle 27 of the actual directionalcontrol valve 10, where the position b is applied, to the piston rodside of the lifting cylinder 7, the actuator-specific pressure reliefvalve 22 of the operational connection of which limits the pressure ofthe operational connection to the preset pressure level. The return oilof the lifting cylinder 7 is guided from the piston side via both thedirectional control valve 23, where the control chart a is applied, andthe choke 26 in parallel with it to the actual control valve, where thepressure medium is guided by the spindle 27 further to an oil tank 14.When the total load is low-lowered, the lowering speed and the magnitudeof pressure peaks caused by accelerations and decelerations dependdecisively on the shape of the spindle 27.

FIG. 3 shows a hydraulic chart when the crane is driven by using themethod and apparatus of the invention in such a manner that theincreased lifting power is applied. When the crane is controlled withthe increased lifting power, in this case at the increased pressurelevel, the control chart b of the directional control valve 24 isapplied and the pressure relief valve 18 is separated from the pressureline 15 of the pump in such a manner that the maximum pressure level ofthe pressure line is defined on the basis of the pressure level set inthe main-pressure relief valve 17 in connection with the actual controlvalve 10. When the lifting cylinder 7 is driven in the direction inwhich the total load is lifted, the pressure medium produced by the pumpis guided via the actuator-specific spindle 27 of the actual controlvalve 10, where the position a is applied, to the piston side of thelifting cylinder 7 in such a manner that the pressure medium passes onlythrough the choke 26 to the operational connection of the cylinder. Thecontrol chart b is applied in the directional control valve 23, wherebythe pressure medium is prevented from passing through the directionalcontrol valve 23. In the choke 26, a pressure loss relative to a volumeflow passing through the choke takes place, limiting the volume flow tothe operational connection of the lifting cylinder 7, i.e. the speed ofmotion of the cylinder. The operational connection of the cylinder isprotected at the raised pressure level primarily so that theactuator-specific pressure relief valve 19 of the actual control valve10, the purpose of which is to protect the pressure medium space betweenthe actuator connection of the actual control valve 10 and the choke 26,is set to a pressure level corresponding to the raised actuator-specificpressure level. In addition, the pressure relief valve 21 used withnormal pressure is separated by closing the directional control valve 25and applying the control chart b, whereby the pressure relief valve 20,the purpose of which is to protect the pressure medium space between thechoke 26 and the piston side of the lifting cylinder 7, is set to apressure level corresponding to the raised pressure level. When thelifting cylinder 7 is driven in the direction in which the total load islowered, the pressure medium produced by the pump is guided via theactuator-specific spindle 27 of the actual directional control valve 10,where the position b is applied, to the space on the piston rod side ofthe lifting cylinder 7, the actuator-specific pressure reliefactuator-specific pressure relief valve 22 of the operational connectionof which limits the pressure of the operational connection to the presetpressure level. The return oil of the lifting cylinder 7 is guided fromthe piston side via the choke 26 to the actual control valve 10, inwhich the pressure medium is guided by the spindle 27 further to the oiltank 14. The directional control valve 23 in parallel with the choke 26,in which valve the control chart b is applied, is closed at theincreased pressure level, and all of the return oil is forced to passthrough the choke 26, whereby in the choke 26 there is a pressure lossrelative to the volume flow passing through the choke, which limits thevolume flow of the return oil from the piston side of the liftingcylinder 7, i.e. the speed of motion of the cylinder. In addition, inthe pressure medium space between the lifting cylinder 7 and the choke26 there is a pressure relief valve 20, which is set to a pressure levelcorresponding to the increased pressure level and, in this example, tothe same pressure level as the actuator-specific pressure relief valve19 of the actual control valve 10. In this example, when the total loadis driven downwards, in addition to pressure caused by the total load onthe piston side of the lifting cylinder 7 there may develop a pressureon the piston rod side of the lifting cylinder 7, which, in the arearatio of the cylinder, also increases the pressure on the piston side ofthe lifting cylinder 7. A combination of these pressures may increasethe pressure of the pressure medium space between the piston side of thelifting cylinder and the choke considerably, wherefore the pressurerelief valve 20 is arranged in the same space to protect the actuator.

At the increased pressure level, particularly when the total load islowered, the lowering speed and the magnitude of pressure peaks causedby accelerations and decelerations depend decisively on the propertiesof the choke 26 and the shape of the spindle 27, whereby the propertiesof the choke 26 are more determinant. When the choke 26 is dimensionedin a proper manner, the lifting and lowering speeds of the load may beadapted at the increased pressure level in such a manner that thepressure peaks caused by accelerations and decelerations do not becomehigher than at the normal pressure level, when the speed of motion ofthe lifting cylinder is higher.

The components included in the auxiliary valve arrangement 11 accordingto the present invention may also be distributed on different sides ofthe crane structure. Likewise, the method and apparatus of the aboveinvention may also be applied to other crane movements, acceleration ordeceleration of which causes similar stress peaks in the structures,such as to control of transfer cylinders or control of an actuator forany other crane movement. The speed reduction according to the inventionmay also be implemented by means of hydraulic series flow control valvesother than the choke. In other words, compared with applying the normallifting power, the invention helps to lower the speed of the actuatorwhen the increased lifting power is applied.

It is obvious to a person skilled in the art that as technologyadvances, the basic idea of the invention may be implemented in variousways. The invention and the embodiments thereof are thus not restrictedto the above examples but may vary within the scope of the claims.

1. A method for controlling an actuator of a crane by control means in asituation where the lifting power of the actuator of the crane isincreased temporarily by an auxiliary valve arrangement, wherein controlproperties of the actuator are changed by means provided in theauxiliary valve arrangement when the temporarily increased lifting poweris applied to limit the speed of the actuator.
 2. A method as claimed inclaim 1, wherein the speed of the actuator is limited in such a mannerthat it does not exceed a predefined maximum value.
 3. A method asclaimed in claim 1, wherein the speed of the crane's lifting cylinder, atransfer cylinder, a cylinder of a boom arrangement extension, acylinder of a crane tool or other similar actuator is limited when thetemporarily increased lifting power is applied.
 4. A method as claimedin claim 1, wherein the control properties of the actuator are changedby means of an actuator-specific series flow control valve, such as achoke.
 5. A method as claimed in claim 4, wherein the control propertiesof the actuator are changed by means of a directional control valve inparallel with the series flow control valve.
 6. A method as claimed inclaim 1, wherein the actuator-specific control properties of theactuator are changed by limiting the flow of hydraulic fluid from theoperation space and/or flowing from the control means of the crane tothe operation space of the actuator.
 7. An apparatus for controlling anactuator of a crane, the apparatus comprising control means forcontrolling the actuators of the crane and at least oneactuator-specific auxiliary valve arrangement for temporarily increasingthe lifting power of the crane, wherein the actuator-specific auxiliaryvalve arrangement also comprises means for changing control propertiesof the actuator in such a manner that the speed of the actuator may belimited.
 8. An apparatus as claimed in claim 7, wherein the controllableactuator is the crane's lifting cylinder, a transfer cylinder, acylinder of a boom arrangement extension, a cylinder of a crane tool orother similar actuator.
 9. An apparatus as claimed in claim 7, whereinthe means for changing the actuator-specific control properties of theactuator comprise a series flow control valve.
 10. An apparatus asclaimed in claim 8, wherein the series flow control valve is a choke.11. An apparatus as claimed in claim 9, wherein the means for changingthe actuator-specific control properties of the actuator also comprise adirectional control valve in parallel with the series flow controlvalve.
 12. An apparatus as claimed in claim 7, wherein the means forchanging the actuator-specific control properties of the actuator arearranged in such a manner that they limit the flow of hydraulic fluidfrom the operation space and/or flowing from the control means of thecrane to the operation space of the actuator.
 13. An apparatus asclaimed in claim 7, wherein the means for changing the actuator-specificcontrol properties of the actuator are arranged between the controlvalve and the piston side of the actuator.
 14. An apparatus as claimedin claim 7, wherein the control means of the crane comprise amain-pressure relief valve, an actuator-specific spindle and one or moreactuator-specific pressure relief valves, which together form the actualcontrol valve of the crane.
 15. An apparatus as claimed in claim 7,wherein the auxiliary valve arrangement comprises a directional controlvalve connected in parallel with a pressure medium space between a pumpand the crane's actual control valve, a pressure relief valve betweenthe directional control valve and a return line of the control valve, adirectional control valve in parallel with a pressure medium spacebetween the actuator and the means, a pressure relief valve between thedirectional control valve and the return line of the control valve, anda pressure relief valve arranged in a pressure medium space between thepiston side of the actuator and the directional control valve.
 16. Anapparatus as claimed in claim 7, wherein the means for changing theactuator-specific control properties of the actuator are or may bearranged in such a manner that the speed of the actuator may be limitedto a predefined maximum value.